“Over the next couple of years somebody’s going to build a game that reaches a billion people,” Bart Decrem, publisher of hit iPhone game Tap Tap Revenge, told a gathering of journalists and toy makers at a briefing in London this week.

That’s a sixth of the world’s population, but as daunting as that is, it’s a feat that’s beginning to look feasible. Angry Birds isn’t far off: Rovio has clocked more than 500 million downloads of its spectacular gaming success.

But Decrem doesn’t work for Rovio. Decrem is Disney’s new head of mobile, and he wants to get there first. But using Disney’s instantly recognisable characters to do so? Too easy.

Disney – no stranger to technology – has a whole array of characters it could launch on to the iPhone App Store. And while it does dabble in this (AppMATes, an iPad app that interacts with toys from the movie Cars 2, was released last year), Decrem doesn’t seem remotely interested in pursuing this.

“For existing IPs [intellectual properties] we still do some of this,” he explains. “They do well but they disappear…the other thing we’re trying to do is build new Disney characters.”

And these new characters have to capture our imaginations like never before. “Smartphones, people love them. They’re fun and beautiful and perfect, and apps that stand out are fun and beautiful and perfect. But how do you stand out on the app store when there are 500,000 apps?”

Decrem’s answer is Where’s My Water? It’s a charming, physics based gamed in the same vein as Cut The Rope. You’ve got to guide the water through a level to reach Swampy, a rather nervous alligator. (You can download it on iPhone and Android).

It’s the big-eyed, bashful star, Decrem says, that has led to Where’s My Water’s success. He won’t talk download numbers, but it’s been the number one paid on the iPhone App Store in 79 countries, and sat at the top in the US for 45 days. To that end, Decrem’s team worked with Disney’s animators to come up with these adorable characters and setting. “The challenge for us is to create new characters, and on new devices.”

Decrem is animated when he speaks – pun very much intended. He’s as far removed from the stuffy, suit wearing Disney middle manager you might expect as possible. Belgian born, he’s already a Silicon Valley legend. He worked on the original Firefox browser, and has sold several companies already: Tapulous to Disney in 2010, and social web browser Flock to Zynga last year.

It’s this background that has helped Decrem give the megacorp’s new division an injection of pragmatism in a famously inflexible Disney (we’ll release our films on DVD when we feel like it, and you’ll like it).

For one, his attitude towards freemium business models is, shall we say, expedient. Where’s My Water still generates most of its revenue from paid-up front versions of the game, but Disney now offers free to play versions on both iOS and Android too. Decrem would rather get maximum eye balls on the game, rather than maximum dollar dollar bill.

“You have to build freemium models, but the great thing is they can reach a lot of players. You can reach a billion people at low cost.”

The end game? “Underneath it all we’re building a network layer,” he says. That network will provide a large, pre-prepared audience for Disney’s next new game – Decrem says new franchises are a priority – giving them a head start on getting to that ten digit audience.

And, Decrem says, they’re already well on the way. “After Angry Birds there’s nothing ahead of us on the app store in terms of cultural phenomenon.” Quite the boast. Alongside a promised high-res Retina Display update for the game on iPad, Disney has commissioned a series of YouTube videos starring Swampy and Bowser-ish antagonist Cranky in the hopes cashing in on this – you can expect other merchandise to follow.

Of course, we reckon Nom would have something to say about Decrem’s claim. But if the candy munching blob is the start of 21st century gaming, he’s got some stiff competition from the biggest media company of last century to contend with.